Hi, Richard, I splited the previous patch for “Enable -Wuninitialized + -ftrivial-auto-var-init for address taken variables” into two separate patches. This is the first one
This first patch is to fix (or work around ) PR103720, therefore it’s an important change, and need to be go into GCC12. At the same time, this patch is the preparation for the second patch that will actually enable -Wuninitialized + -ftrivial-auto-var-init for address taken variables. The reason I separate the previous patch into two is: most of the previous concern was on the second part of the patch (the change in tree-ssa-uninit.c), I don’t want those concern prevent this first patch from being approved into GCC12. In this part, I addressed your comments in gimplify.c : ===== tree decl_name + = build_string_literal (IDENTIFIER_LENGTH (DECL_NAME (decl)) + 1, + IDENTIFIER_POINTER (DECL_NAME (decl))); you need to deal with DECL_NAME being NULL. ===== Please also see the detailed description below for the problem and solution of this patch. This first patch has been bootstrapped and regressing tested on both X86 and aarch64. Okay for GCC12? Thanks. Qing. ================================= Change the 3rd parameter of function .DEFERRED_INIT from IS_VLA to decl name. Currently, the 3rd parameter of function .DEFERRED_INIT is IS_VLA, which is not needed at all; In this patch, we change the 3rd parameter from IS_VLA to the name of the var decl for the following purposes: 1. Fix (or work around) PR103720: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103720 As confirmed in PR103720, with the current definition of .DEFERRED_INIT, Dom transformed: c$a$0_6 = .DEFERRED_INIT (8, 2, 0); _1 = .DEFERRED_INIT (8, 2, 0); into: c$a$0_6 = .DEFERRED_INIT (8, 2, 0); _1 = c$a$0_6; which is incorrectly done due to Dom treating the two calls to const function .DEFERRED_INIT as the same call since all actual parameters are the same. The same issue has been exposed in PR102608 due to a different optimization VN, the fix for PR102608 is to specially handle call to .DEFERRED_INIT in VN to exclude it from CSE. To fix PR103720, we could do the same as the fix to PR102608 to specially handle call to .DEFERRED_INIT in Dom to exclude it from being optimized. However, in addition to Dom and VN, there should be other optimizations that have the same issue as PR103720 or PR102608 (As I built Linux kernel with -ftrivial-auto-var-init=zero -Werror, I noticed a bunch of bugos warnings). Other than identifying all the optimizations and specially handling call to .DEFERRED_INIT in all these optimizations, changing the 3rd parameter of the function .DEFERRED_INIT from IS_VLA to the name string of the var decl might be a better workaround (or a fix). After this change, since the 3rd actual parameter is the name string of the variable, different calls for different variables will have different name strings as the 3rd actual, As a result, the optimization that previously treated the different calls to .DEFERRED_INIT as the same will be prevented. 2. Prepare for enabling -Wuninitialized + -ftrivail-auto-var-init for address taken variables. As discussion in the following thread: https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577431.html With the current implemenation of -ftrivial-auto-var-init and uninitialized warning analysis, the uninitialized warning for an address taken auto variable might be missed since the variable is completely eliminated by optimization and replaced with a temporary variable in all the uses. In order to improve such situation, changing the 3rd parameter of the function .DEFERRED_INIT to the name string of the variable will provide necessary information to uninitialized warning analysis to make the missing warning possible. gcc/ChangeLog: 2022-01-10 qing zhao <qing.z...@oracle.com> * gimplify.c (gimple_add_init_for_auto_var): Delete the 3rd argument. Change the 3rd argument of function .DEFERRED_INIT to the name of the decl. (gimplify_decl_expr): Delete the 3rd argument when call gimple_add_init_for_auto_var. * internal-fn.c (expand_DEFERRED_INIT): Update comments to reflect the 3rd argument change of function .DEFERRED_INIT. * tree-cfg.c (verify_gimple_call): Update comments and verification to reflect the 3rd argument change of function .DEFERRED_INIT. * tree-sra.c (generate_subtree_deferred_init): Delete the 3rd argument. (sra_modify_deferred_init): Change the 3rd argument of function .DEFERRED_INIT to the name of the decl. gcc/testsuite/ChangeLog: 2022-01-10 qing zhao <qing.z...@oracle.com> * c-c++-common/auto-init-1.c: Adjust testcase to reflect the 3rd argument change of function .DEFERRED_INIT. * c-c++-common/auto-init-10.c: Likewise. * c-c++-common/auto-init-11.c: Likewise. * c-c++-common/auto-init-12.c: Likewise. * c-c++-common/auto-init-13.c: Likewise. * c-c++-common/auto-init-14.c: Likewise. * c-c++-common/auto-init-15.c: Likewise. * c-c++-common/auto-init-16.c: Likewise. * c-c++-common/auto-init-2.c: Likewise. * c-c++-common/auto-init-3.c: Likewise. * c-c++-common/auto-init-4.c: Likewise. * c-c++-common/auto-init-5.c: Likewise. * c-c++-common/auto-init-6.c: Likewise. * c-c++-common/auto-init-7.c: Likewise. * c-c++-common/auto-init-8.c: Likewise. * c-c++-common/auto-init-9.c: Likewise. * c-c++-common/auto-init-esra.c: Likewise. * c-c++-common/auto-init-padding-1.c: Likewise. * gcc.target/aarch64/auto-init-2.c: Likewise. ******The complete patch is attached:
0001-Change-the-3rd-parameter-of-function-.DEFERRED_INIT-.patch
Description: 0001-Change-the-3rd-parameter-of-function-.DEFERRED_INIT-.patch
